A Fusidium Disease of Xylaria in Wisconsin

Abstract

SUMMARYFusidium parasiticum Westendorp, apparently previously unreported in the United States, has been found inciting a destructive disease of Xylaria oxyacanthae stromata at Madison, Wisconsin.The fungus appears in late spring in the form of white, downy mildew-like lesions on the Xylaria stromata. As the disease progresses, the infected stromata become shrunken and disintegrate without maturing ascospores.The fungus has been isolated and studied in pure culture. Of the various media on which cultivation of the organism was attempted, corn meal agar and Xylaria decoction agar supported the best mycelial growth, and these were the only substrates upon which sporulation was obtained in vitro.Flask cultures of four Wisconsin species of Xylaria were inoculated with spore suspensions and mycelium from agar culture of Fusidium parasiticum. Moderate infection of the X. oxyacanthae stromata was obtained, and the parasite was reisolated from the lesions on the host.In microtome sections through diseased Xylaria specimens the most profuse development of the Fusidium mycelium was observed to be in the area outside the ectostroma, but hyphae may penetrate to the very center of the host.Bacterial pockets are commonly found associated with the Fusidium lesions. The bacteria involved are interpreted as secondary invaders.Initial damage to the interior of the stroma is mild, even when the mycelium has penetrated deeply. There is, however, a marked tendency toward ascocarp abortion in later stages of infection.The parasite produces septate, sparingly-branched conidiophores which bear long chains of hyaline, fusoid conidia. Haematoxylinstained preparations revealed conidia, conidiophore cells, and cells of the mycelium to be uninucleate.